<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/less">
        @bg:pink;
        @px:200px;
        #app{
          width: 400-@px;
          height: 100px;
          background:@bg
        }
    </style>
    <!--运行时编译-->
    <script src="//cdnjs.cloudflare.com/ajax/libs/less.js/2.5.3/less.min.js"></script>
</head>
<body>
    <div id="app">

    </div>
</body>

</html>